To dilate stenosed blood vessels, bile ducts, etc. in vivo, stent insertion into the stenosed area has been performed, as shown in the following examples:
(1) A balloon-tipped catheter is inserted into the stenosed area. The thus dilated area is kept dilated with a stent which is inserted through another balloon-tipped catheter (2-step method); and
(2) Without a preliminary dilative step, a balloon-tipped catheter carrying a stent is inserted so that the area dilated by the balloon is kept dilated with the stent (1-step method).
For these conventional techniques, metallic stents (made of stainless steel, tantalum, etc.) have been used.
These metallic stents lack flexibility and are likely to cause stress to the ducts (e.g., blood vessels) in vivo. Because of these features, the use of conventional stents involves the following problems; (1) a possibility of causing inflammation and excessive hypertrophy of the stent-inserted area, leading to a recurrence of stenosis, and (2) permanent retention of the stent as foreign matter in vivo.
To avoid the stress caused by metallic stents, the use of stents made of resin has been considered. Stents made of resin cause less stress to the ducts in vivo. However, they are difficult to form into a desired shape. Furthermore, it is difficult to attach a resin stent to a balloon-catheter in a compressed condition, to expand the stent at the stenosed area and to keep it expanded. To overcome these shortcomings of resin stents, a proposal for stents made of shape-memory resin has been made (Japanese Patent Application Disclosure No. 1991-21262). If a stent made of shape-memory resin is used, it is possible to expand the stent within the stenosed area, but it is not always easy to control the degree of stent expansion precisely. Furthermore, such a stent also remains permanently in vivo, continuing to cause stress to the ducts in vivo (e.g., blood vessels), although the stress may not be severe.
The present invention is aimed at providing such a device for dilating ducts in vivo that involves no risk of causing restenosis and that does not remain in vivo indefinitely. The invention is additionally aimed at providing a method for manufacturing such a device.